[TowerTalk] Noob question re: Thrust Bearings

[K9MA]

There's some controversy about whether the thrust bearing should support 
the vertical load. It's primary purpose is usually to take the radial 
load. If the mast is free to move vertically, of course, the rotator 
bearings take all the vertical load. If the mast is fixed vertically at 
both the thrust bearing and the rotator, there is a risk that, because 
it is overconstrained, large stresses and/or binding could result. 
Everything has to be aligned almost perfectly to prevent this. Assuming 
the rotator can handle the vertical load, I think it's better to allow 
the mast to move vertically in the thrust bearing by tightening the 
bolts (with locknuts) just enough to prevent radial motion.

If the rotator CAN'T handle the vertical load, then great care must be 
taken that the thrust bearing entirely supports the mast. That means 
allowing some vertical play at the rotator.

73,
Scott K9MA


On 5/9/2020 14:01, Tom WA9WSJ via TowerTalk wrote:
>   Another way to help prevent and mast slippage would be to attach a muffler clamp onto the mast just on top of the thrust bearing.My two towers have had this going on 20 years now and no slippage.
> Tom
>      On Saturday, May 9, 2020, 12:24:20 PM MDT, scott at nx7u.net <scott at nx7u.net> wrote:
>   
>   I've never found any clear explanation of how thrust bearings are
> practically implemented.
> If the bearing is to "hold up" the antenna (so that the rotator doesn't
> have to), I assume that it's the force from the four radially-oriented
> bolts that do so?  It seems to me that over time the mast would slip.
> Is that really not an issue with sufficient bolt torque?
> It seems to me that the mast should be pinned through the bearing
> instead--that is, a through-bolt that goes through holes drilled in the
> mast.
> What obvious (but not to me) thing am I missing?
> Thanks,
> NX7U
> 45 years active & never had a rotator bigger than Radio Shack :-)
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-- 
Scott  K9MA

k9ma at sdellington.us